I love library dining rooms. How many do you hope to have eat at the table most times? If only four I would add a small round table with four parson slipcovered chairs centered under the light. A couple of wall shelves flanking the door shown in the last picture and either a built in cushioned window seat or a purchached long bench in the bow window for listening to the piano or curling up with a book. If you do not like the bench in the window a small club chair or two in corners are nice in a multipurpose dining room as well.